1. Field of the Invention
The present invention relates to a multimedia system built up by a plurality of unit terminals and to a navigation unit terminal serving as a unit terminal configuring part of the multimedia system.
2. Description of the Related Art
A program for on-board type control equipment of a vehicle was the latest one when purchased by a user but has been getting old with an elapse of a usage period, resulting in such a case that the latest function provided by a supplier can not be performed. Therefore, the user needs to update the program for the control equipment. Such being the case, there was disclosed a technology (refer to, e.g., Japanese Patent Laid-Open Publication No. 2005-202503) of supplying (downloading) a control program of the latest version provided from the supplier into the control equipment within the vehicle possessed by the user in a way that utilizes radio waves for a mobile phone. The program for the control equipment mounted on the user's vehicle is updated by this technology.
Disclosed further is a technology (refer to, e.g., Japanese Patent Laid-Open Publication No. 2006-209417) related to an efficient program transmission on the occasion of updating the program. This technology is that a should-be-updated program is compared with a new program by use of a checksum system in a plurality of blocks organizing the program, and only a block portion with the checksum proving not to be identical as a result of the comparison is transmitted for the update. With this scheme, a size of the program that should be transmitted for the update can be reduced, and the program can be efficiently transferred.
Other technologies related to the update of the program are disclosed in Japanese Patent Laid-Open Publication Nos. 2005-233930, 2001-75967, H11-296364 and 2004-295542.